The study investigators conducted a retrospective cohort study of Chinese individuals with MS (n=33), NMOSD (n=31), and ADEM (n=18). Brain and spinal cord magnetic resonance imaging (MRI) scans were obtained of all participants. Subsequently, 2 neurologists examined the MRI scans independently to determine lesion characteristics. In the study, the rostrum and genu were described together as the callosum “forepart”; the isthmus was considered part of the body.

Lesion distribution, shape, and spreading shape was established. All quantitative data were assessed with the chi-squared test.

Lesions in the forepart of the corpus callosum were more common in patients with MS (69.7%) than patients with NMOSD (51.6%) or ADEM (22.2%). Patients with NMOSD (77.4%) more often had lesions in the callosal body compared with patients with MS (60.6%) or ADEM (55.6%). Splenial lesions were observed with similar frequency in patients with MS (54.5%) and NMOSD (54.8%), although less often in patients with ADEM (33.3%).

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Compared with MS and NMOSD, ADEM lesions occurred less frequently in the rostrum and genu (P =.002). According to mid-sagittal images, ovoid lesion shapes were most common in MS (45.5%), radial lesions were more frequent in NMOSD (41.9%), and lesionswith other shapes were most likely to be associated with ADEM (61.1%).

NMOSD and ADEM lesions were more likely to have a diffuse distribution (P =.006; P =.033) and blurred margins (P <.001; P =.017) compared with MS. Lesions with heterogeneous intensity occurred more often in NMOSD than MS (P =.016) and ADEM (P =.001).

Callosal lesions in MS tended to have a focal distribution and clear margins compared with NMOSD and ADEM lesions. Such characteristics may facilitate correct diagnosis with MRI scans, according to the investigators.